Types of Microphones

 There are a number of different types of microphones. These differences can be divided into two areas:

1. The type of conversion technology the microphone uses, in other words, the technical method the microphone uses to convert sound waves into electricity or audio signal. The most common technologies, with specific advantages and disadvantages, are:

    1.1 Dynamic

    1.2 Condenser

    1.3 Ribbon

    1.4 Crystal

2. The type of application they are designed for, with specific characteristics:

    2.1 Directional properties

    2.2 Frequency response

    2.3 Impedance

1. Microphones according to their type of conversion technology

1.1 Dynamic Microphones (coil motion)

This type of microphone is sturdy, resilient to rough handling, versatile and ideal for general-purpose use. They are well suited to handling high volume levels, have no internal amplifier and do not require batteries or external power.

1.2 Condenser Microphones (electrostatic capacitance)

These microphones have a stronger signal, are more sensitive and responsive compared to a dynamic microphone. They are well-suited to capture subtle nuances in a sound, but not ideal for high-volume work as their sensitivity can cause them to distort sound. These microphones require power from a battery or an external source (48V phantom power). 

1.3 Ribbon Microphones (conductor)

These are a type of dynamic microphones however they are built in a different way. A dynamic microphone has the diaphragm attached to a moving coil vibrating in a magnetic filed. A ribbon mic features instead, a thin strip of metal suspended in a strong magnetic field. The ribbon acts both as the diaphragm and the transducer element itself, providing then the same kind of sensitivity as a condenser mic. These microphones are delicate in fragile due to the ribbon material that is suspended in the magnetic gap. They are highly detailed and more affected by lower frequencies than louder ones. They naturally produce a perfect figure-of-eight polar pattern and respond to EQ extremely well.

1.4 Crystal Microphones (twisting or bending of a piezoelectric crystal)

These microphones use a piezoelectric crystal as its transducer. These crystals are durable and cheap and have a relatively large electrical output. They are inadequate for quality sound recording and are commonly used in telephones and portable sound systems. 

2. Microphones according to the application they are designed for

2.1 Directional properties/Microphone Polar Patterns

2.1.1 Omnidirectional - general and unfocused, picks sound evenly from all directions. It is usually used for capturing ambient noise, situations where the sound is coming from multiple directions, or situations where the mic position must remain fixed while the sound source is moving. They are prone to monitor feedback which makes them unsuitable for loud and noisy venues but very suitable for studios or venues with great acoustics (like churches for example).

2.1.2 Unidirectional - picks up sound predominantly from one direction. This includes cardioid and hypercardioid microphones.

        2.1.2.1 Cardioid - "heart-shaped" pick-up pattern, sound is picked up mostly from the front and sides to a lesser extend. It emphasises sound from the direction of the mic whilst leaving some latitude for mic movement and ambient noise. It is ideal for a live performance and other situations where noise reduction and feedback suppression are needed. 

        2.1.2.2 Hypercardioid - an exaggerated version of the cardiod microphone. It is very directional and eliminates most sound from the sides and rear. It isolates the sound from a subject or direction when there is a lot of ambient noise, but while removing all this the sound can sometimes feel a little unnatural. When handling these one must be careful to keep the sound consistent.

        2.1.2.3 Shotgun microphones - also called Line and Gradient, feature a tube like design that make their polar pattern even more directional than the hypercardioids. They have a tighter polar pattern up front with a longer pickup range.

2.1.3 Bidirectional - Uses a figure-of-eight pattern and picks up sound from two opposite directions, front and back, while rejecting the sides. One use for this mic is an interview when two people are facing each other.

2.2 Frequency response or the way a microphone responds to different frequencies

It is a characteristic that depending on the microphone, some frequencies are exaggerated and others are attenuated. A microphone's frequency response pattern is shown using a chart (above) and referred to as a frequency response curve. The x axis shows the frequency in Hertz and the y axis shows the response in decibels.

A flat frequency response produces the "purest audio", this means that the microphone is equally sensitive to all frequencies - no frequencies would be exaggerated or attenuated.

Frequency response is usually displayed as a range between two figures. For example, a microphone that says to have a frequency response between 20Hz and 20kHz can reproduce all frequencies within this range, frequencies outside this range will be reproduced to a much lesser extent or not at all. 

Note: Condenser microphones generally have a flatter frequency response compared to a dynamic microphone, this means that a condenser mic is often more desirable if capturing accurate sound is the prime objective. 

2.3 Impedance

Impedance is an electronics term which measures the amount of opposition a device has to an AC current. Impedance is the combined effect of capacitance, inductance and resistance on a signal. Impedance, often displayed with the letter Z (Hi-Z or Low-Z) is measured in ohms, shown with the Greek Omega symbol Ω.

In regards to microphones, there are three general classifications for microphone impedance:

    1. Low Impedance (less than 600Ω)

    2. Medium Impedance (600Ω - 10,000Ω)

    3. High Impedance (greater than 10,000Ω)

Microphones with a hard-wired cable and a jack connector are high impedance, microphones with a separate balanced audio cable and XLR connectors are low impedance. High-impedance microphones are usually cheap and their main disadvantage is that they do not perform well over long distance cables, in particular a loss of the high frequencies. Low impedance microphones are usually the preferred choice. 

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